Computational methods of gas radiative noise for hypersonic vehicles

When a vehicle flies at high velocity, the high temperature gas in shock layer undergoes strong physical and chemical change along with substantive optical radiation which will directly affect the imaging quality of an infrared seeker. Fluid dynamics Navier-Stokes equations with thermo-chemical non-equilibrium models were used to simulate the high temperature gas flow. Narrowband model accounting for both electronic and vibrational-rotational transition mechanisms was employed to obtain gas radiative characteristics. Radiative transfer equation was computed by finite volume method to acquire radiative intensity distribution. Based on validation of flow solver, radiative parameter calculation and radiative transportation computation, hypersonic flight vehicles were simulated. Flow structures and parameters and particles distributions were obtained. Emission coefficients in specific wavelength range were solved through the flow parameter. The distribution of the coefficients shows that is very similar to shock wave shape and gas temperature contours behind the shock. Gas radiative noises on optics window are axisymmetric, which is strongly related to flow velocity, gas species and so on. When Mach number increases, the gas radiative noises grow rapidly.